Alzheimer Disease (AD) is a neurodegenerative disease which causes dementia. The terms “Alzheimer Disease” and “Alzheimer's Disease” are both utilized in the art, these terms being equivalent and are used interchangeably here and elsewhere. The period from first detection of AD to termination can range from a few years to 15 years, during which time the patient progressively suffers loss of both mental function and control of bodily functions. There is significant variability in the progress of the disease. While the majority of patients have a gradual, inexorable progression (losing on average 3 to 4 points on the 30 point Folstein mini-mental state score annually), approximately 30% of AD cases have a prolonged stable initial plateau phase lasting several years, as described in Haxby et al. (1992), herein incorporated by reference. A subgroup of patients has a fulminant, rapidly progressive downhill course over several years, as described in Mann et al. (1992), herein incorporated by reference. Other patients (about 10% of cohorts) remain slowly progressive, showing only gradual decline from year to year, as described in Grossi et al. (1988), herein incorporated by reference. The pathological, chemical and molecular bases of this heterogeneity remain undetermined. Recognition of the variability of AD progression represents an important clinical insight, and may explain the diagnostic difficulties presented by “atypical” cases.
Attempts at predicting the onset of AD or monitoring its progression have met with limited success. While in certain cases, there is a familial manifestation of the disease, it appears that the majority of AD cases are non-familial, and until recently (see below), no simple genetic marker for the disease had been determined. Much research has focused on the protein beta-amyloid, deposits of which are found in the brains of AD victims.
However, recently, as described in our related U.S. patent (U.S. Pat. No. 6,210,895Apr. 3, 2001 and publication (Schipper et al., 2000), both herein incorporated by reference, we have devised a diagnostic method, useful in the prediction, diagnosis, and prognostication of AD, AACD/MCI, and related neurological diseases. This diagnostic method is based on the determination that patients suffering from AD have a significantly lower concentration of heme oxygenase-1 (HO-1) in their lymphocytes and plasma, and, accordingly, a significantly lower concentration of ribonucleotide sequences encoding HO-1 in their lymphocytes.
HO-1: Heme oxygenase-1 (HO-1) is an enzyme that catalyses the rapid degradation of heme to biliverdin in brain and other tissues. This 32 kDa member of the heat shock protein superfamily contains a heat-shock element in its promoter region and is rapidly up regulated in response to oxidative stress, metal ions, amino acid analogues, sulfhydryl agents, and hyperthermia. In response to oxidative stress, induction of HO-1 may result in protection of cells by catabolizing pro-oxidant metalloporphyrins, such as heme, into bile pigments (biliverdin, bilirubin), with free radical scavenging capabilities. Heme and other intracellular ferrous iron chelates are capable of converting hydrogen peroxide to the highly cytotoxic hydroxyl radical.
Using immunostaining techniques in conjunction with laser scanning confocal microscopy, intense HO-1 immunoreactivity in neurons and astrocytes of post-mortem hippocampus and temporal cortex derived from AD subjects has been observed, whereas neural HO-1 staining was faint or non-existent in the hippocampus and temporal cortex of control specimens matched for age and post-mortem interval, as noted in Schipper et al. (1995), herein incorporated by reference. Furthermore, consistent co-localization of HO-1 to neurofibrillary tangles and senile plaques in the AD specimens has been demonstrated. Finally, robust 32 kDa bands corresponding to HO-1 were observed by Western blotting of protein extracts derived from AD temporal cortex and hippocampus after SDS-PAGE, whereas control HO-1 bands were faint or absent. These results indicate that HO-1 is significantly over-expressed in neurons and astrocytes of AD hippocampus and cerebral cortex relative to control brains and support the contention that AD-affected tissues are experiencing chronic oxidative stress.
AACD/MCI: AACD and MCI are terms used to identify individuals who experience a cognitive decline that falls short of dementia. These terms are equivalent, MCI being a more recently adopted term, and are used interchangeably throughout this application. Satisfaction of criteria (World Health Organization) for this diagnosis requires a report by the individual or family of a decline in cognitive function, which is gradual, and present at least 6 months. There may be difficulties across any cognitive domains (although memory is impaired in the vast majority of cases), and these must be supported by abnormal performance on quantitative cognitive assessments for which age and education norms are available for relatively healthy individuals (i.e., the patient is compared to normal subjects his/her own age). Performance must be at least 1 SD below the mean value for the appropriate population on such tests. Neither dementia, nor significant depression or drug effects may be present. No cerebral or systemic disease or condition known to cause cerebral cognitive dysfunction may be present. In Applicant's experience, all patients who were classified as CDR.5 (“questionable dementia”) on the Clinical Dementia rating scale and who met these exclusions, also met the criteria for AACD/MCI. About ⅓ of Alzheimer's patients have had a clearly definable period of isolated memory deficit which preceded their more global cognitive decline, as noted by Haxby et al. (1992), herein incorporated by reference. Using AACD/MCI criteria which look at other domains in addition to memory, the percentage with an identifiable prodrome is likely higher. Fortunately, not all AACD/MCI individuals seem to decline. It appears that a significant number of these subjects show a stable, non-progressive memory deficit on testing.
Related Disorders: Determining HO-1 concentration can also assist in predicting, diagnosing, or prognosticating other dementing diseases having similar manifestations and/or in distinguishing such diseases from AD. Such other diseases include Parkinson disease with dementia, Progressive Supranuclear Palsy, Vascular (i.e. multi-infarct) Dementia, Lewy Body Dementia, Huntington's Disease, Down's syndrome, normal pressure hydrocephalus, corticobasal ganglionic degeneration, multisystem atrophy, head trauma, neurosyphilis, Creutzfeld-Jacob disease and other prion diseases, HIV and other encephalitides, and metabolic disorders such as hypothyroidism and vitamin B12 deficiency. The method may also prove useful in differentiating the “pseudodementia” of depression from Alzheimer disease.
The determination of a relationship between HO-1 levels and AD represents a very significant advance in this field, and may be utilized for the development of methods of predicting, diagnosing in its very early stage, and prognosticating AD and other dementing diseases. However, identification of the factor(s) and mechanism(s) which control HO-1 expression in the normal versus the diseased state are needed, to provide even earlier diagnosis, as well as therapeutic methods and reagents or substances, and methods and reagents for the study of AD and other dementing diseases. In addition, the reduction or absence of HO-1 in patients suffering from AD represents a negative test, and, particularly for the purposes of diagnosis, it would be more desirable to have a positive indicator of disease, i.e. a factor whose presence (rather than absence) correlates with disease. Further, the decrease in HO-1 expression may represent an effect, rather than a cause of AD and other dementing diseases, therefore the identification of factor(s) and mechanism(s) which control HO-1 expression in the normal versus the diseased state are also needed to identify components and events which have an active causative role in the onset and progression of these diseases.